The natural gas production and transmission industry routinely wastes significant amounts of energy that could be put to economical and environmentally friendly use for the production of electrical energy. The need for electric power at the well site, compressor stations, downstream city gate and neighborhood distribution stations is well known. Flow measurement, equipment status, valve actuation, emission control and communication systems all require different but typically small amounts of electrical energy to operate. Even when grid electric power is available, commercial electrical power may not be desirable to use due to setup and permitting costs. In these and remote situations where grid power is not available, solar panels or thermoelectric generators are typically used.
When gas comes to the surface from a well, it is often at a pressure significantly higher than pressure which may be safely placed in a transmission line. Accordingly, the gas pressure typically is regulated or choked down to the transmission line pressure limit. This pressure reduction releases large amounts of energy, typically as a cooling effect, which is wasted and in many cases has to be reversed by burning gas to reheat the cooled gas before it can continue down the pipeline. When high pressure transmission gas arrives at what is referred to as a “city gate,” the pressure must again be reduced significantly before it can enter pipelines that go into the neighborhoods. Again, the “pressure” energy in the gas is typically wasted even though electric power is needed for instrumentation and communication systems at the site. At remote locations, solar power or thermoelectric systems are often used to keep batteries charged to operate the equipment.
Solar energy is essentially free power, but its production is unreliable in many parts of the world due to uncontrollable weather conditions. This unpredictability results in the solar systems being greatly oversized in both panels and battery banks to provide the required safety factor. Also, solar systems by their nature allow batteries to be deep drawn which reduce the battery life.
Thermoelectric systems operate 24/7 off the natural gas in the line so over sizing and deep drawing batteries are not a problem, although the cleanliness and quality of the gas greatly affects the operation of the systems and often requires high maintenance “gas cleaning” before it may be used to run the thermoelectric generator. This is particularly a problem at well sites where the gas has not yet been cleaned up.
A generating device which would not be weather, sunlight or gas quality dependant and which would use the previously wasted pressure differential seen at well sites and city gate stations would be useful in the industry for supplying electric power to keep battery banks at full charge regardless of weather or gas quality.
Also, industry standards applicable to equipment placed in a potentially hazardous environment require that faults in the equipment would be unlikely to cause an explosion or fire in the area even if explosive gasses were present at the time of the equipment failure. For such a requirement, isolating the electrical circuits from the potentially explosive media with fixed barriers and static seals is highly desirable.
The prior art includes a variety of turbines having integrated generators. U.S. Pat. No. 4,293,777 discloses a turbine with a hollow rotor in which are disposed the elements of an electric generator. U.S. Pat. No. 4,935,650 discloses a fluid driven rotor with spaced apart ferromagnetic discs which cooperate with cavities of a ferromagnetic stator to generate electrical power. U.S. Pat. No. 2,984,751 discloses a rotor carrying an armature element which cooperates with exteriorly mounted stationary field elements. U.S. Pat. No. 3,039,007 discloses a turbine wheel having a shaft which mounts a permanent magnet for being rotatably driven inside a stator steel core. U.S. Pat. No. 2,743,375 discloses a turbo-generator having rotating bladed discs alternating with stationary discs: each of the discs carry cooperating flat radial pole-pieces and windings. U.S. Pat. No. 3,157,793 includes stator discs circumferentially disposed about rotor discs which have magnetic poles placed about their peripheries. U.S. Pat. No. 5,118,961 discloses a hollow rotor driven on it's periphery about a stator steel core.
Prior art integrated turbines include electrical generator elements that are in the turbine media or are separated from that media by dynamic seals. Isolation of a pressurized turbine drive mechanism from a generator using a magnetic drive is possible, but magnetic drives are both expensive and subject to magnetic decoupling and runaway under load, which may destroy a bearing in short order.
The disadvantages of the prior art are overcome by the present invention, and an improved differential pressure electrical generator powered by fluid pressure in the flow line is hereinafter disclosed.